Field of the Invention
The present invention relates to a wound stator, more particularly to a wound stator for a vehicle alternating-current generator.
Description of Related Art
An alternating-current generator is used for converting mechanical energy into alternating-current electric energy. In a vehicle alternating-current generator, the output power of an engine drives a rotor of the generator to rotate within a stator to convert mechanical energy of the engine into electric energy to charge a storage battery, which then supplies electric energy to electrical parts of a vehicle.
A vehicle alternating-current generator typically has an annular stator and a rotor. By means of rapid rotation of the rotor in the stator, magnetic fields are formed by wires wound on the stator so as to generate an induced electromotive force (voltage) in the wires. In general, the voltage output by the alternating-current generator is proportional to the number of coil groups in a stator ring. Therefore, the higher the density of wires wound on a stator ring, the higher the power generation of the generator.
Folding and winding are usually used for a coil winding in a conventional generator. To achieve high power generation, a large number of coils are used, and thus the winding and folding become complex. Furthermore, a large stator ring is required for such winding to provide sufficient space for the coils. However, the conventional windings have disadvantages. For example, the width of the elongated groove of the stator ring has to be large to receive a number of wires and the received wires are inevitably disorderly arranged, which results in a number of air gaps. FIG. 1 is a partial sectional view of a conventional stator winding, where each groove 11 in a stator 1 receives multiple wires 13 and slant lines represent air gaps between wires and groove walls or between different wires. These air gaps result in an undesirable increase of magnetic resistance which lowers power generation efficacy. In addition, since the stator ring is large, the corresponding rotor also has to be large so that the two can fit each other, which increases the size of the generator that comprises them. A large generator will limit the usable space of a vehicle.
U.S. Pat. No. 8,296,926 discloses a small-sized stator of an alternating-current generator having high wire density in a groove of the stator. In the stator, copper wires with rectangular cross-sections (a flat copper wire) are required. The copper wires are bent into U-shaped/V-shaped wire units, which thereafter are inserted in the grooves of a stator ring, and the ends of the wire units are then soldered two by two to form a circuit. Accordingly, the wires are orderly arranged so as to effectively reduce air gaps, increase wire density, and decrease magnetic resistance (see FIGS. 10 and 11). However, many wire ends will jut out from the stator ring. For example, in a stator ring having 96 grooves in which each groove has two wire units, after wire insertion is completed, there are a total of 384 wire ends and 192 solder joints, and the process for manufacturing such stator may be complex. In addition, the flat copper wire used in such stator may be more expensive than a round copper wire.
Given the above, there is need for a stator that is miniature, easy to manufacture and has high power generation efficacy with low cost and a generator having such stator.